The marking of ceramic materials, glazes and glasses can be effected by conventional marking and decoration methods such as etching, cutting, engraving, grinding or by applying a glass or glaze colorant. In these methods, the surface of the marked material is altered with the consequence that the material may suffer damage, especially if marking is effected by etching, engraving, or cutting. The application of a glass or glaze colorant necessitates, in addition, a second firing step. The markings so produced are not always satisfactory in all respects.
It is also known to mark glass by means of a laser beam, whereas the known methods are based on melting or removing substrate material such that the surface of the marked material is also altered.
German Offenlegungsschrift 3 539 047 postulates a method of decorating, marking, and engraving enameled objects using laser beams by incorporating into the enamel coating opacifying agents which the laser beam causes to decompose optically and locally; for example, oxides of titanium, tin, cerium, and antimony. A drawback of this method is that, for example, transparent enameled objects cannot be marked because the opacifying agent incorporated in the enamel coating does not change optically at the non-irradiated areas and, therefore, strongly influences the overall appearance of the object. Furthermore, the opacifying agent employed may adversely affect the mechanical properties of the enamel.
Industry has sought to surface mark glass, ceramic, porcelain, metal, plastics, and the like with four physical attributes. These four attributes are high-resolution, high-contrast, permanence, and speed.
Well known efforts to date have only produced two or three of these attributes. For example, kiln marking ceramics using glass frit material at kiln temperatures ranging from 100.degree. to 1000.degree. C. results in high-resolution, high-contrast, permanent indicia on ceramics, glass, and metals. These known processes require heating the entire substrate along with the glass frit or metal oxide marking material in a kiln. The problem with these processes is the time factor and energy consumption are not commercially efficient to create the indicia. Time factors ranging from minutes to hours are common. Energy consumption of a kiln is generally measured in kilowatts per ton and/or BTUs per pound. Furthermore, these processes do not lend themselves to portability.
Another known marking method is peening on metal. This method cannot be used on glass, ceramic, or other brittle materials because of surface damage and/or breakage. Where used, this method produces a high-resolution, permanent, fast surface indicia. However, high contrast marks are not produced.
Other known marking methods are ink printing methods. One state of the art transfer printing method is taught by WO 95/13195 (May 1995) to Meneghine et al. assigned to Markem Corporation. These methods use a laser-transferable ink on a plastic carrier. The ink is mixed in a transfer medium solution in order to enhance the conversion of laser (IR) energy to heat. These methods produce a high-resolution, high-contrast, and relatively fast method. There is a UV cure step which is time consuming. The problem with this and all ink methods is a lack of permanence. Acids and other solvents remove ink from a hard surface. This method teaches curing the ink onto the substrate surface. The present invention teaches bonding a marking medium to form a new marking layer atop the substrate surface rather than transferring an ink to the substrate and then curing the ink.
Another well known marking method teaches the use of ink jet printers. In order to improve application performance, appearance and permanence, environmentally hazardous solvents are mixed with the ink. Even with these hazardous solvents however, significant improvement has not been achieved.
U.S. Pat. No. 4,541,340 (1985) to Peart et al. discloses a printing process for marking fabrics or plastics in a permanent image. Sublimable dyes are used such as nitroso dyes. A diffusion of the dyestuff into the substrate is caused by a pressurized air step on a transfer label. Only application to fabrics and plastics is taught. The chemistry is different from the present invention. However, the result of a permanent high contrast mark is claimed.
Another related group of marking methods is laser combined with glass frit or metal oxide marking mediums. U.S. Pat. No. 4,769,310 (1988) to Gugger et al. teaches first creating a glaze in a kiln process. The glaze has a radiation sensitive additive in amounts ranging from 0.01 to 30% by weight. This glaze is then irradiated by a beam of Nd:YAG pulsed laser having light pulses of six to eight nanoseconds at a wavelength of 0.532 .mu.m and a pulse content of 250 milli-joules. The problem with this method is the burden of creating a time consuming glaze surface before applying the high-speed laser beam.
U.S. Pat. No. 5,030,551 (1991) to Herren et al. teaches a laser-based method to mark ceramic materials, glazes, glass ceramics, and glasses by first applying to a workpiece a 100 to 10,000 Angstrom thick transparent layer of titanium dioxide. Second, the workpiece is fired in an oven at 620.degree. C. for one minute and then slowly cooled in the closed oven. Third, the layer is irradiated with a pulsed laser in accordance with the form of the marking to be applied. The laser light must have a wavelength which is sufficiently absorbed by the oxide layer so that a discoloration of the oxide layer is produced at the irradiated areas. The problem with this method is the time and energy-consuming step of firing and cooling the workpiece.
The method of the present invention makes it possible to produce a direct and rapid marking that is indelible and which is, therefore, abrasion and scratch-proof. The markings obtained are also corrosion-proof, solvent-resistant, dimensionally stable, free from deformation, fast to light, heat, and weathering, easily legible, and have good contrast and very good edge definition. In addition, there is virtually no impairment of the mechanical, physical, and chemical properties of the marked material, e.g. mechanical strength and chemical resistance.
There has now been found a flexible method which makes it possible to mark metals, plastics, ceramic materials, glazes, glass ceramics and glasses without damaging the surface thereof and without specific requirements being made of the substrate, which method comprises the use of a glass frit based or mixed organic materials or mixed metal oxide layer for the laser marking.
Accordingly, the present invention relates to a method of laser marking metals, plastics, ceramic materials, glazes, glass ceramics and glasses of any desired form which comprises applying to the substrate material a marking material which, depending upon its principal components, may or may not contain at least one energy absorbing enhancer then irradiating said marking material layer with a laser or diode based energy such that the radiation is directed onto said layer in accordance with the form of the marking to be applied, and using laser or diode based energy of a wavelength which is sufficiently absorbed by the marking material so that a bonding occurs on the substrate , thereby forming a marking layer atop the substrate.